1. Technical Field
The invention relates to a method for controlling vacuum in an intake conduit in a combustion engine of a vehicle wherein actuation of the brake booster closes a throttle in the intake conduit to provide the brake booster with vacuum.
2. Background of Related Art
Modern vehicles normally use a brake booster connected to the brake pedal in the brake circuit of the vehicle in order to amplify the pressure that is required for actuating the brakes. When a driver actuates the brake pedal, the brake booster supplies an hydraulic pressure corresponding to the actuating force applied to the pedal by the driver to the brake circuits of the vehicle, thereby actuating the brake calipers or drums of the vehicle. The brake booster is controlled by a source of vacuum. This source is usually the intake conduit of the engine of the vehicle.
The intake conduit is provided with a throttle valve that is controlled by an accelerator pedal via an engine control system. The throttle valve controls the amount of air supplied to the cylinders. It also cooperates with the fuel injection system to control the air/fuel ratio needed for a required power output. The vacuum required for the brake booster is taken from a position downstream of the throttle valve.
Under certain running conditions, such as a cold start combined with a high load or during stratified combustion with the throttle wide open, the vacuum downstream of the throttle valve may not be sufficient for proper operation of the brake booster. It is therefore a problem to provide a sufficient vacuum to the brake booster under all operating conditions of the engine.
One solution to this problem is shown in EPO 833,044-A2 wherein a sensor is used for monitoring the vacuum in the brake booster. When a pressure level is detected at which the vacuum is insufficient for actuation of the brake booster, the engine will switch from stratified to homogenous combustion. This will cause the throttle to be controlled to create a vacuum in the intake conduit. A drawback of this solution is that the engine will switch between different operating conditions as soon as the pressure in the brake booster passes a set level, whether it is required or not.
A further solution is shown in WO 99/54,613-A1. According to this solution, when an actuation of the brake pedal is detected, a counter starts measuring the period of time that the pedal is being actuated. If the period exceeds a set time, the engine is switched from a lean to a rich air/fuel ratio causing the throttle to be controlled so that a vacuum is created in the intake conduit. A problem with this solution, however, is that there is a delay between the actuation of the brake pedal and the switching between operating conditions of the engine. This causes a corresponding delay before a vacuum can be supplied to the brake booster.
Other known solutions use specially provided air pumps, operated separately from the engine to supply a vacuum for the brake booster. This requires the mounting of an additional pump on the vehicle. This pump must be driven by the engine, requires additional space, and is an extra cost to be added to the manufactured product.
The present invention solves the above problems by providing a method using direct control by demand. The goal is to switch the engine between different operating conditions only when the brake pedal is actuated.
The present invention relates to a method for controlling the vacuum in an intake conduit of a combustion engine in a vehicle that is provided with a brake booster and a pedal for actuating the booster. Actuation of the brake pedal when the engine is operated with stratified combustion will control the throttle valve in the intake conduit to create a vacuum for the brake booster. The throttle valve is controlled to close instantly, for example within a few tenths of a second, in order to create a vacuum in the intake conduit as quickly as possible.
When the driver actuates the brake pedal, an electrical signal is generated for controlling the throttle valve via a control unit. This can be achieved either by closing an electrical contact as soon as the pedal begins to move, or by using the signal that is generated by the actuation of an electrically controlled brake pedal that has no mechanical connection with the brake booster and its associated master brake cylinder. The throttle valve is preferably electrically controlled by an electronic control unit. This control unit is either connected to, or integrated with the engine control system.
As soon as the vacuum in the brake booster has reached a predetermined level, or when the electrical signal indicating brake pedal actuation ceases, the throttle valve can be opened.
The method may be used under several different operating conditions where the vacuum in the intake conduit is insufficient. One such operating condition is cold starting, when the emissions of, for instance, hydrocarbons (xe2x80x9cHCxe2x80x9d) from the engine reaches their highest level. In order to heat a catalytic converter in the exhaust system quickly, it is desirable to increase the engine load by opening up the throttle and leaving it open. The result can be that the vacuum in the intake conduit is too low to give the necessary brake servo effect. If not acted upon, this could cause a loss of a major part of the braking effect during start-up.
As a rule, the vehicle brakes are not operated immediately after the engine is started. The supply of vacuum to the brake booster may therefore be delayed until the need arises. Hence the warm-up cycle of the engine and the catalytic converter can proceed without interference for a longer period of time. This will help reduce the emissions of HC and other pollutants.
By connecting the control unit to a speed sensor and sensors for the brake anti-locking system (ABS), a further embodiment enables the warm-up cycle of the engine and the catalytic converter to continue undisturbed as the procedure is only performed when the vehicle is moving or if the anti-locking system is activated. The latter may occur for instance if the vehicle anti-slip system uses the ABS-system to brake one or more wheels.
When the driver actuates the brake pedal and the procedure is started, the engine control unit must make sure that the drivability of the vehicle does not deteriorate due to such things as misfire and variations in engine speed. As the throttle valve starts to close, it is necessary to adjust the ignition timing and/or the amount of injected fuel.